Various types of low-profile operating switch panels have been already proposed. For example, there are low-profile operating switch panels having structures as shown in FIG. 1 and FIG. 5.
In a switch panel SP1 shown in FIG. 1, a plurality of metal domes 12 to be disposed at electrodes 11 on a substrate 10 are fixed with a film 14 adhered to the substrate 10 via an adhesive layer 13.
Here, the metal dome 12 is usually made of an elastic hemispheric cap of metal. Moreover, as shown in FIG. 2 for example, the metal dome 12 is disposed on an electrode 11 including a pair of an arc electrode layer 11a and a straight electrode layer 11b guided therein (a thickness of this layer is made slightly lower than the electrode layer 11a, or an insulating layer is provided thereon). In a free state as shown in FIG. 3, if a user presses the metal dome 12 from above the film, then the cap is crushed down and a switch is turned on as shown in FIG. 4. When a finger is released, the cap restitutes and the switch is turned off.
Meanwhile, in a switch panel SP2 shown in FIG. 5, a plurality of metal domes 12 to be disposed at electrodes 11 on a substrate 10 are fitted into relevant holes 15a on a spacer film 15 and fixed with a film 14 adhered to the spacer film 15 via an adhesive layer 13.
In any cases, upon pressing the above-described metal dome 12, air inside the dome is naturally compressed and thereby generates repulsion. Therefore, in order to provide the user with comfortable operation feeling, the air inside the dome needs to be evacuated temporarily out of the dome.
Accordingly, since each of the metal domes 12 constitutes an independent sealed space in the switch panel SP1 in FIG. 1, air escape holes (not shown) communicating with the inside of the dome are provided on the adhesive layer 13 and on the film 14, or alternatively, such an air escape hole is provided on the substrate 10, where the air inside the dome is set open to outside air.
However, if such an air escape hole is provided and the air inside the dome is set open to the outside air, there is a problem that humidity or dust in the outside air is caught into the switch panel SP1.
Meanwhile, regarding the switch panel SP2 in FIG. 5, the spacer film 15 can be simply placed on the substrate 10. Then, upon pressing the metal dome 12, the air compressed inside the dome is dispersed temporarily in the periphery thereof through gaps under the spacer film 15. Therefore, the switch panel SP2 has an advantage that provision of an air escape hole is not particularly required, and so forth.
However, installation of the spacer film 15 incurs an increase in the number of components and an increase in assembly steps, whereby a cost rise is incurred. Moreover, there is also a problem that a thickness, a weight or the like of an end product is also increased. Needless to say, another problem of catching humidity or dust in the outside air is also incurred if peripheral portions of the spacer film 15 are made open to the outside air.